The present invention relates to lactic acid bacteria capable of preventing colonization of intestinal cells by Giardia intestinalis, or to a culture supernatant thereof, respectively, for use in the treatment and/or prophylaxis of disorders associated with the colonization of the gut by Giardia intestinalis. The present invention also pertains to strains of Bifidobacterium having the above traits and to the use of lactic acid bacteria for the preparation of an ingestable carrier, such as a food or pharmaceutical composition, for the treatment and/or prophylaxis of an infestation of the intestine by Giardia intestinalis. 
Giardia intestinalis is a flagellate protozoan which upon infestation of an individual's gut may effect disorders such as abdominal pains, loose stool or even severe diarrhea. Its life cycle has two stages, cysts and trophozoites, which different forms allow the microorganism to survive in different and even adverse environments.
Cysts are dormant, quadrinucleate and ovoid forms responsible for transmission of giardiasis. After ingestion of cysts by an individual, excystation is triggered by exposure to gastric acid and/or digestive enzymes. The parasite thus emerging, which is termed trophozoite, is binucleate and half-pear shaped having a size of around 10 μm with a broad anterior and a narrow posterior side. The ventral side is by and large covered by the ventral disk which is deemed to at least in part account for an attachment of the trophozoite to the intestinal surface
After excystation trophozoites may persist in the small intestine of the infected individuum for a long time amounting even to years. If trophozoites are carried downstream by the flow of intestinal fluid they again start to encyst to adapt to a new environment.
Cysts are excreted with the faeces and may withstand a variety of extreme environmental conditions, including different temperature, pH and tonicity conditions. An infected individual may secrete about 9×108 cysts per day, with doses to as low as 10 cysts proved to be sufficient to produce infection in another individual. Transmission of Giardia intestinalis may be accomplished in a variety of different ways with the main routes of transmission being waterborne and foodborne. Person to person spread is supported by some daycare and nosocomial outbreaks. In addition, wild animals are found to be infectious reservoirs of Giardia intestinalis and may contribute to a spread of the pathogen.
Giardiasis, like other intestinal diseases, is more severe in infants and children. Infection is normally associated with diarrhea and malabsorption resulting in an impaired growth and development of the child and may eventually also lead to the death of newbornes.
Around one half of infected people are, however, asymptomatic and contribute to the spread of the pathogen, since due to the absence of any perceptible symptoms no corresponding regimen is applied.
Though a great deal of scientific effort has been invested on the investigation of Giardia intestinalis pathogenesis of giardiasis could not be explained by means of a single virulence factor alone and no toxic compound has been isolated so far.
The light microscopic appearance of a gut colonized by Giardia has been found to be rather variable ranging from a normal mucosal structure to a subtotal villous atrophy. Results of electron microscopy investigations revealed ultrastructural changes such as shortening and disruption of microvilli (Chávez et al., Experimental Parasitol. 80 (1995), 133-138).
Such structural abnormalities have been found to be accompanied by a reduction in lactase, sucrase and maltase activities in the microvillus membrane as well as to an impaired intestinal transport (Buret et al., Gastroenterology 103 (1992), 506-513; Roberts-Thomson et al, Gastroenterology. 71 (1976), 57-61).
In addition to the two forms illustrated above Giardia intestinalis has developed an extremely changing surface structure and has evolved a family of protective proteins that cover all exposed surfaces (Aley et al., Infect. Agents Dis. 4 (1995), 161-166; Müller, et al., Infect. Immun. 64 (1996), 1385-1390; Nash et al., J. Euk. Microbiol. 42 (1995), 604-609). These variable surface proteins (VSPs) protect trophozoites from both immunological and environmental factors, such that Giardia may evade the host's defenses and may survive in a highly degradative environment such as is prevailing in the intestinal tract of mammals. A modification in the VSPs occurs at about every 6th to 13th generation making it difficult or nearly impossible for the host's immune system to develop a specific response against the pathogen. Immune and environmental stress can select different VSP phenotypes. Furthermore, antigen switching of VSPs after excystation has also been reported (Gillin et al., Annu. Rev. Microbiol. 50 (1996), 679-705).
Human giardiasis is associated with an increase in the number of lamina propria and intraepithelial lymphocytes suggesting that T-cell activation could be responsible for micro villous damage. However, induced immunosuppression in mice resulted in a more profound effect on microvillous associated enzymes as compared to non-immunosupressed animals, indicating that during an infection by Giardia intestinalis epithelial damage seems not be dependent on immune function alone.
A common therapy of giardiasis is the administration of antibiotics, such as those belonging to the class of nitroimidazoles. Yet, in endemic areas the response to therapy has been shown to be rather inconsistent (Katelaris et al., Aliment. Pharmacol. Ther. 8 (1994), 187-192). Moreover, due to the at least in part destruction of the intestine's natural microflora, the administration of such antibiotics is always accompanied by severe side effects such as extended diarrhea or even an expanded infestation of the gut by other detrimental microorganisms, such as yeast.
Hence, there is a need in the art for additional options to treat giardiasis or means to prevent infestation of an individual by the pathogen.
The problem of the present invention therefore resides in providing additional means for the treatment or prophylaxis of an infection by Giardia intestinalis. 